The lemonade diet is a master cleanse and will release toxins into your body. Depending on how many toxins are in your body you could experience some symptoms. Some of theses symptoms could be:

Headaches
Dizziness
Nausea
General feeling of being tired.

How many if any of these symptoms you experience, depends on how many toxins you have in your body, more toxins, more symptoms. How many of these symptoms you experience is also related to how closely you follow the diet.